Medical Lab Technology

Egg of H. nana in a wet mount stained with iodine.

Hymenolepiasis is caused by two cestodes (tapeworm) species, Hymenolepis nana (the dwarf tapeworm, adults measuring 15 to 40 mm in length) and Hymenolepis diminuta (rat tapeworm, adults measuring 20 to 60 cm in length). Hymenolepis diminuta is a cestode of rodents infrequently seen in humans and frequently found in rodents.

Eggs of Hymenolepis nana are immediately infective when passed with the stool and cannot survive more than 10 days in the external environment

Hymenolepis nana is the most common cause of all cestode infections, and is encountered worldwide. In temperate areas its incidence is higher in children and institutionalized groups

Hymenolepis nana and H. diminuta infections are most often asymptomatic. Heavy infections with H. nana can cause weakness, headaches, anorexia, abdominal pain, and diarrhea.

H. nana eggs are oval and smaller than those of H. diminuta, with a size range of 30 to 50 µm. On the inner membrane are two poles, from which 4-8 polar filaments spread out between the two membranes. The oncosphere has six hooks.

Hymenolepis nana (preferred name now Rodentolepis nana) is common in humans because of multiple routes of infection. Humans can be infected by ingesting eggs from mouse or human faecal contamination, or by ingesting insects which are intermediate hosts.

Picture courtesy Anam Mustafa